The present invention relates to temperature measuring systems and more particularly to commercially useful combustion turbine thermocouple systems in which the high gas temperature to be measured is estimated from signals generated by the thermocouple which is being operated in the gas stream but is cooled to operate at lower tolerable temperatures.
High gas inlet temperatures in combustion turbines have been measured with the use of thermocouples such as the ANSI type K (Chromel Alumel alloy by Hoskins Manufacturing Company) which has a reliable operating temperature up to about 2200.degree. F. Life expectancy of the thermocouple is shortened or limited by melting when it is operated at higher gas temperatures.
The use of thermocouple (TC) cooling to obtain estimated measurements of higher gas temperatures thus enables (1) the measurement of gas temperatures which are near or above the TC melting point and (2) a substantial and economizing extension of TC operating life in the measurement of higher gas temperatures which are below the TC melting point and above the reliable operation temperature limit of the TC.
The basic operation of a TC system, in which high temperatures are estimated, involves some form of periodic cooling of the TC and a computation of the actual gas temperature from multiple TC signals taken over a period of time during which the TC is exposed to the hot gas without cooling.
In a January 1977 Engineering For Power article entitled "The Pulsed Thermocouple for Gas Turbine Application" by J. Odgers, D. Kretschmer and A. F. Schlader, there is described an experimental type system in which a mechanical method of TC cooling is employed. The TC is inserted into a hot gas stream when temperature signals are to be generated and recorded, and the TC is withdrawn from the hot gas stream for cooling before it reaches its designated limit operating temperature. While mechanical cooling of this kind is workable, it is not desirable in industrial applications like combustion turbines. In the Odger et al. article, the concept of estimating the actual gas temperature by extrapolation from the transient TC readings is set forth and validated for accuracy of the estimating procedure. Basically, an analog electric circuit employs operational amplifiers which require an extensive calibration procedure to enable the estimations to be made.
In a 1976 NASA paper entitled "A New Approach to the Pulsed Thermocouple for High Gas Temperature Measurements" by G. E. Glave, H. A. Will and L. N. Krause, there is described a system in which hydrodynamic TC cooling is employed (with the use of a small singularly dedicated local air cooling tube) and in which the extrapolation computation is carefully verified (with the use of time consuming statistical methods). However, the system described is basically a laboratory-type system in which an off-line computer is used to make the temperature extrapolation. Obtaining temperature estimates is thus time consuming and impractical for operating industrial equipment.
While the prior art demonstrates the validity of the basic concepts described, there has been no system developed which is characterized with TC coolant control and data acquisition and processing which enables rapid temperature measurement and rapid cycling for multiple temperature measurements as needed in combustion turbine and other industrial applications.